Monday, 31 August 2015

A Natural Hour-Glass of Amalgam

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In 1874 the Spang collection of minerals held this specimen -

"One of the most curious specimens is a natural amalgam of silver. It is a dodecahedral crystal, one-half an inch by three-eighths in size, which communicates, by a solid rod of the same material passing through the interior of the rock and nearly concealed from view, with a similar crystal of amalgam. When placed in such a position that one crystal is vertically above its mate, and allowed to stand for a short time, the mercury finds its way downward and distends the lower crystal until its faces are quite obliterated. In fact, it is converted into a pear-shaped drop, and looks as if it were about to fall from the crystal. When the specimen is inverted and allowed to remain so for half an hour, the mercury percolates through the solid mass of amalgam, the distended crystal acquiring its former definite outlines, and settles into a drop depending from the apex of crystal No. 1. This lusus naturæ, an hour-glass of metallic crystals, is, I believe, without parallel."

The whole article, from Popular Science Monthly, February 1874, detailing the Spang mineral collection follows -

THE SPANG COLLECTION OF MINERALS.

By ALBERT R. LEEDS,

PROFESSOR OF CHEMISTRY IN THE STEVENS POLYTECHNIC INSTITUTE.

THE increasing taste for the pursuit of natural science in this country is strikingly exhibited by the rapid increase in the number of gem and mineral collections. The taste is not confined to men of any one profession, but is cultivated by lawyers, physicians, artists, engineers, iron-masters and persons in every rank and walk of life. Some of the collections thus formed are valuable in a scientific point of view, on account of their being receptacles for specimens obtained in the prosecution of mining enterprises, or from local discoveries arising in the opening of quarries, the development of farm-lands, or cutting of canals and road-ways; thus preserving material which otherwise would be lost, and which ultimately must be handed over to the skilled mineralogist for accurate description and analysis. Other private collections are of deep interest on account of containing specimens of such exceeding rarity and costliness as to surpass aught that our colleges with their hitherto meagre endowments can display. This is especially true of the magnificent cabinet, some few of whose wonders I desire cursorily to describe in the present sketch, and which, by very general consent, is regarded as one of the finest collections in existence at the present time. This result has been achieved by an unsparing expenditure of money, time, and energy, not only in this country and Europe, but in every part of the world; extending to the sending out of paid collectors, the blasting of rocks in remote mountain-districts, the outbidding of all rivals when cabinets were offered for sale, and an unceasing watch over the fate of every unique specimen known to mineralogists. In some instances entire collections were purchased in order to secure a few remarkable specimens. To the man of science the collection affords the gratification of examining fine specimens of bodies so extremely rare that few persons have ever beheld them. The resources of the cabinet are most generously placed at the disposal of those engaged in any special mineral research; and, finally, the munificent owner proposes eventually to endow some institution of learning in this country with the perfected cabinet.

It is difficult to begin where so many objects worthy of study present themselves, and I shall not attempt a systematic description of this accumulation of minerals, which, though crowded together, can barely find room in eleven cases of drawers, a fire-proof safe and six glass show-cases. In the inclosed cases are more than 300 drawers, averaging about 25 specimens to the drawer.

But in the first place the tourmalines attract our attention. Of these, a variety found near Gouverneur, in the State of New York, is distinguished by its peculiar brown color and internal structure. There is a suite of at least one hundred specimens of this variety alone, each one having been selected on account of some characteristic difference, and presenting together all the known and probably some yet undescribed crystalline faces. Some of the specimens are aggregates of crystals, one mass displaying fifty distinct terminations; others are individual crystals, frequently doubly terminated and showing the different arrangement of the planes upon the analogous and antilogous poles. The dimensions of one of these single crystals, reputed to be the largest ever found at Gouverneur, deserve a permanent record. It is four inches in height and four and a half inches through, with the rhombohedral faces of one termination almost perfectly developed, and with one rhombohedral face of the other termination four inches in width, the two other corresponding planes having been points of attachment to the rock. It is bounded by eighteen prismatic faces, all of which are perfect in form and polish.

Of the black tourmalines, there is one from Springfield, New Hampshire, which has a termination remarkable for the extreme development of the basal plane. It is 41⁄2 x 33⁄4 inches across, and almost extinguishes the primary rhombohedron. Among entirely unique specimens from Greenland, Bovey Tracey, in Devonshire, England, Haddam, Connecticut, Norway and Sweden, we might mention a group from Greenland, of fifty or sixty crystals, mostly doubly terminated, and from four to six inches in length, forming a rosette with divergent crystals.

To the finely colored red tourmalines, which are frequently cut and polished as gems, the name of rubellite is given; those from Siberia being mostly violet red, the Brazilian rose-red; the specimens from Chesterfield and Goshen, Massachusetts, are pale rose-red and opaque; those from Paris, Maine, fine ruby-red. Among these rubellites there are six from Elba, of exquisitely delicate pink-color. They are hexagonal prisms, one of which is one and a quarter inch in height and three quarters of an inch in diameter, all implanted on a base that is itself very beautiful from the contrasted groups of rock-crystal, adular, and rosettes of mica, of which it is made up. Of rubellites from Elba there are more than fifty specimens, some of them reposing upon the native rock; others are terminated detached crystals of various shades of pink—also crystals on the gangue and fine detached rubellites from Siberia. When it is remembered that the slightest imperfection in the sharpness of an edge or angle, the scratching of a single face, excludes a specimen from this cabinet, and that none are admitted which are not at the same time remarkable for size, beauty, and perfection of crystalline form, the brilliant effect of a drawer filled with these natural gems can be imagined.

More than usual interest attaches to the mineral of which I am now about to speak, the Columbite, on account of the derivation of its name and the history of its discovery. The rare metallic element columbium, or niobium as it has subsequently been called, was first discovered in 1802, by Hatchett, in a specimen of this mineral sent out by Governor Winthrop, of Connecticut, to Sir Hans Sloane, then president of the Royal Society, and the original analysis was made by Wollaston, with an accuracy truly surprising, upon only four grains of the specimen, so long ago as the year 1809. It is highly probable that Governor Winthrop's mineral came from Middletown, Connecticut, at which locality some very large crystals have since been found; among many such in the Spang collection, there is one composed of twenty-five crystals compounded together, and showing the terminal planes at the summit of each crystal. Two of the prismatic faces of one of these crystals are three inches in length.

There is a genus of minerals termed zeolites, from a Greek word signifying to boil, for the reason that when heated the large percentage of water which they contain escapes with intumescence, and of these one of the most remarkable species is scolecite, so called because, on touching it with the tip of a blow-pipe flame, it curls up like a worm. I find elsewhere the record of some crystals, which were found in the Berufiord, Iceland; and which exceeded two inches in length and were a quarter of an inch thick. There is a radiated mass of scolecite crystals in this collection, brought from Poonah, Hindostan, the largest being three inches in length, and compounded of two twins, each of which is one-quarter of an inch in diameter. The beauty of this group is still further enhanced by clusters of transparent tabular apophyllites attached to the sides of the crystals.

There is another species of zeolite, which, on account of its brilliant, pearly lustre, has received the name of stilbite. Usually its color is white; in this collection there is a specimen of stilbite from Poonah, that is compounded of a great number of individual crystals, the terminations of which together make up an octahedral summit with planes two inches wide. The color is a deep, rich salmon.

Of the apophyllites from the same locality, one of the most beautiful is a tabular square prism with the angles replaced by octahedral planes, all of which are perfect in lustre and surface polish. The crystal measures two and a quarter inches across, and is one and a quarter inch in height. There are remarkable suites of pink apophyllites from the Hartz, transparent green crystals, highly modified, from Nova Scotia, and some of the finest of those crystals which made the Erie tunnel through the trap-rock of Bergen Hill, New Jersey, at one time so famous among mineralogists. It is from such wonderful works as these that we are enabled justly to appreciate the transcendent skill with which Nature performs her task when she tries her hand at the plastic arts; for example, what piece of statuary could be so faultless, in grouping and finish, as one of these specimens, which consists of thousands of apophyllite crystals, many of them an inch and averaging half an inch in size, festooned about a cluster of pendant stalactites?

Two uncut diamonds of great brilliancy are remarkable for the perfection of their forms; one is an octahedron with dodecahedral planes, the other is an elliptic twin, in shape closely resembling a heart. Each stone is of one carat weight, and entirely limpid and without a flaw—fit, in fact, for setting, though never touched by the lapidary. Less costly, but hardly less beautiful than these, are some Aragonites from Sicily, which are strikingly thrown into relief by the pedestal of lemon-yellow crystals of sulphur upon which they are mounted. They are six-sided prisms, measuring two and a quarter inches along the vertical, and two and a half inches along the lateral axis. Their bases and summits are perfectly plane.

At the time of its purchase and incorporation into the museum of Harvard University, I had the pleasure of critically examining the collection of minerals which had been accumulated by Herr Liebner, a mining-captain in the Tyrol. The finest specimens were a suite of Tyrolese epidotes, and I imagined that Nature could not surpass them, until I saw those in the possession of Mr. Spang. Among others of still larger dimensions, there is one prism of epidote which is eight inches in length, and three-quarters by one half an inch in thickness. It is perfectly straight, and all its sides and terminal planes are of a smoothness and lustre indescribable. The light transmitted through the crystal in one direction is a magnificent ruby-red, almost identical in tint with that exhibited by light-red silver-ore. Another crystal might fairly be entitled a gem of immense size; it is three inches in length, and exhibits thirteen terminal planes. On revolving it into different positions, the light passing through it changes in color from a delicate hair-brown to cherry and then to deep ruby-red.

Before concluding this sketch, some bodies of extreme rarity should be mentioned, among them the chloro-carbonate of lead, termed phosgenite. Most mineralogists are rejoiced to obtain minute crystals of this mineral, the large crystals from Crawford, near Matlock, in Derbyshire, having sold for from fifteen to twenty pounds sterling each. This cabinet contains a perfect prism, of strong adamantine lustre on all its faces, which is one and a half inch in height, one and a quarter broad, and one and an eighth in thickness. Still more rare is a mineral, of which singularly enough we possess as yet no satisfactory analysis, known as Turnerite, from the Tavetsch Valley in the Alps. In this collection there is a number of perfect crystals, five if I remember correctly, each of which displays many highly-lustrous facets, and occurring both isolated and embedded in a rock made up of quartz and albite. The largest crystal is three-quarters of an inch long and five-eighths of an inch thick. It is a doubly-terminated hexagonal prism, the basal edges being regularly replaced by twelve small planes. The color is a translucent green—in most other recorded cases it is yellow or brown.

One of the most curious specimens is a natural amalgam of silver. It is a dodecahedral crystal, one-half an inch by three-eighths in size, which communicates, by a solid rod of the same material passing through the interior of the rock and nearly concealed from view, with a similar crystal of amalgam. When placed in such a position that one crystal is vertically above its mate, and allowed to stand for a short time, the mercury finds its way downward and distends the lower crystal until its faces are quite obliterated. In fact, it is converted into a pear-shaped drop, and looks as if it were about to fall from the crystal. When the specimen is inverted and allowed to remain so for half an hour, the mercury percolates through the solid mass of amalgam, the distended crystal acquiring its former definite outlines, and settles into a drop depending from the apex of crystal No. 1. This lusus naturæ, an hour-glass of metallic crystals, is, I believe, without parallel.

Then there is a resplendent crystal of axinite from Switzerland, among multitudes of others, which is three inches upon one of the faces and four inches measured along its greatest dimension; and a cluster of stibnite crystals from Hungary, weighing perhaps five pounds, of which the largest crystal is a prism three inches long and three-eighths of an inch thick, perfectly terminated.

In conclusion, the emeralds deserve our admiration, as they would that of persons least sensible of natural beauty. Of these, there is a number of large crystals, some mounted upon the rock in which they occur, others detached. Some of the latter from Bogotá have highly-modified terminations. Although not so large as the others, being but one-half an inch in length and three-eighths of an inch in thickness, by far the finest emerald is one which is implanted, along with smaller crystals, upon a piece of rock from the Ural Mountains. It has a perfect termination, presenting very many rhombohedral and pyramidal planes. Without a flaw, absolutely limpid, and of wonderful purity and depth of color, it is a natural gem, in the eyes of a mineralogist incomparably more beautiful than any cut and polished jewel could be. Its history might suggest to the writer of fictions some features of a romance, it having been given by a Czar of Russia to Taglioni, and subsequently placed by her in pawn with a wealthy gentleman in Paris.

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